Cosmology: A Research Briefing

Panel on Cosmology

Board on Physics and Astronomy

Commission on Physical Sciences, Mathematics, and Applications

National Research Council

National Academy Press
Washington, D.C.
1995



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Cosmology: A Research Briefing Cosmology: A Research Briefing Panel on Cosmology Board on Physics and Astronomy Commission on Physical Sciences, Mathematics, and Applications National Research Council National Academy Press Washington, D.C. 1995

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Cosmology: A Research Briefing NOTICE: The project that is the subject of this report was approvedby the Governing Board of the National Research Council, whose membersare drawn from the councils of the National Academy of Sciences,the National Academy of Engineering, and the Institute of Medicine.The members of the panel responsible for the report were chosen fortheir special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors accordingto procedures approved by a Report Review Committee consisting ofmembers of the National Academy of Sciences, the National Academyof Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuatingsociety of distinguished scholars engaged in scientific and engineeringresearch, dedicated to the furtherance of science and technologyand to their use for the general welfare. Upon the authority of thecharter granted to it by Congress in 1863, the Academy has a mandatethat requires it to advise the federal government on scientific andtechnical matters. Dr. Bruce Alberts is president of the NationalAcademy of Sciences. The National Academy of Engineering was established in 1964, underthe charter of the National Academy of Sciences, as a parallel organizationof outstanding engineers. It is autonomous in its administrationand in the selection of its members, sharing with the National Academyof Sciences the responsibility for advising the federal government.The National Academy of Engineering also sponsors engineering programsaimed at meeting national needs, encourages education and research,and recognizes the superior achievements of engineers. Dr. HaroldLiebowitz is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the NationalAcademy of Sciences to secure the services of eminent members ofappropriate professions in the examination of policy matters pertainingto the health of the public. The Institute acts under the responsibilitygiven to the National Academy of Sciences by its congressional charterto be an advisor to the federal government and, upon its own initiative,to identify issues of medical care, research, and education. Dr.Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was established by the National Academyof Sciences in 1916 to associate the broad community of science andtechnology with the Academy's purposes of furthering knowledge andadvising the federal government. Functioning in accordance with generalpolicies determined by the Academy, the Council has become the principaloperating agency of both the National Academy of Sciences and theNational Academy of Engineering in providing services to the government,the public, and the scientific and engineering communities. The Councilis administered jointly by both Academies and the Institute of Medicine.Dr. Bruce Alberts and Dr. Harold Liebowitz are chairman and vicechairman, respectively, of the National Research Council. This project was supported by the National Aeronautics and SpaceAdministration (NASA) under Grant No. NAGW-3304. Front Cover: The anisotropy of the temperature of the cosmic microwave backgroundradiation, as mapped by the Differential Microwave Radiometer onNASA's Cosmic Background Explorer satellite. Red shades representhotter fluctuations, and blue and black shades represent cooler fluctuations.(Courtesy of the COBE team and NASA.) Back Cover: Looking back in time with NASA's Hubble Space Telescope (HST). The HST's Wide-Field Planetary Camera (WFPC2) captured this image of galaxiesas they were billions of years ago. Many objects are irregular andill-formed compared to nearby galaxies, showing the evolution offorms of galaxies between the distant past and times closer to thepresent. The size of the image is 75 arc seconds, and the total exposuretime is 15 hours. (Courtesy of Edward Groth, Jerome Kristian, andmembers of the WFPC2 team.) Additional copies of this report are available from: Board on Physics and Astronomy HA 562 National Research Council 2101 Constitution Avenue, NW Washington, DC 20418 Copyright 1995 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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Cosmology: A Research Briefing PANEL ON COSMOLOGY MARC DAVIS, University of California at Berkeley, Chair BLAS CABRERA, Stanford University SANDRA M. FABER, University of California, Santa Cruz MARGARET GELLER, Harvard-Smithsonian Center for Astrophysics JACQUELINE N. HEWITT, Massachusetts Institute of Technology RICHARD KRON, Yerkes Observatory, University of Chicago PHILIP M. LUBIN, University of California, Santa Barbara STEPHAN S. MEYER, University of Chicago JEREMIAH P. OSTRIKER, Princeton University Observatory DAVID N. SCHRAMM, University of Chicago DAVID WILKINSON, Princeton University DONALD C. SHAPERO, Director ROBERT L. RIEMER, Senior Program Officer

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Cosmology: A Research Briefing BOARD ON PHYSICS AND ASTRONOMY DAVID N. SCHRAMM, University of Chicago, Chair ROBERT C. DYNES, University of California, San Diego, Vice Chair LLOYD ARMSTRONG, JR., University of Southern California DAVID H. AUSTON, Rice University DAVID E. BALDWIN, Lawrence Livermore National Laboratory PRAVEEN CHAUDHARI, IBM T.J. Watson Research Center FRANK DRAKE, University of California, Santa Cruz HANS FRAUENFELDER, Los Alamos National Laboratory JEROME I. FRIEDMAN, Massachusetts Institute of Technology MARGARET GELLER, Harvard-Smithsonian Center for Astrophysics MARTHA P. HAYNES, Cornell University WILLIAM KLEMPERER, Harvard University ALBERT NARATH, Sandia National Laboratories JOSEPH M. PROUD, GTE Corporation (retired) ROBERT C. RICHARDSON, Cornell University JOHANNA STACHEL, State University of New York at Stony Brook DAVID WILKINSON, Princeton University SIDNEY WOLFF, National Optical Astronomy Observatories DONALD C. SHAPERO, Director ROBERT L. RIEMER, Associate Director DANIEL F. MORGAN, Program Officer NATASHA A. CASEY, Program Assistant STEPHANIE Y. SMITH, Project Assistant

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Cosmology: A Research Briefing COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS RICHARD N. ZARE, Stanford University, Chair RICHARD S. NICHOLSON, American Association for the Advancement of Science, Vice Chair STEPHEN L. ADLER, Institute for Advanced Study SYLVIA T. CEYER, Massachusetts Institute of Technology SUSAN L. GRAHAM, University of California, Berkeley ROBERT J. HERMANN, United Technologies Corporation RHONDA J. HUGHES, Bryn Mawr College SHIRLEY A. JACKSON, Rutgers University KENNETH I. KELLERMANN, National Radio Astronomy Observatory HANS MARK, University of Texas at Austin THOMAS A. PRINCE, California Institute of Technology JEROME SACKS, National Institute of Statistical Sciences L.E. SCRIVEN, University of Minnesota LEON T. SILVER, California Institute of Technology CHARLES P. SLICHTER, University of Illinois at Urbana-Champaign ALVIN W. TRIVELPIECE, Oak Ridge National Laboratory SHMUEL WINOGRAD, IBM T.J. Watson Research Center CHARLES A. ZRAKET, MITRE Corporation (retired) NORMAN METZGER, Executive Director

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Cosmology: A Research Briefing Preface The Board on Physics and Astronomy (BPA) is reassessing the areasof physics that were examined by the Physics Survey Committee inits report, Physics Through the 1990s (National Academy Press, Washington, D.C., 1986). One of the eightvolumes of the report, Gravitation, Cosmology, and Cosmic-Ray Physics, was the subject of a National Research Council program initiationmeeting that I chaired in 1992. At that meeting, the need for reassessmentsin the areas of cosmology, neutrino astrophysics, and cosmic-rayphysics was identified. The Panel on Cosmology, along with the Committee on Cosmic-Ray Physicsand the Panel on Neutrino Astrophysics, is part of this updatingeffort. Because of the connection to astrophysics and astronomy,the BPA has coordinated with the Committee on Astronomy and Astrophysics(CAA) in the conduct of this study. The panel is chaired by MarcDavis, who also chairs the CAA. The research briefing format is intended to provide advice to programmanagers and policy makers on the opportunities for scientific advancesin a frontier field. The field of cosmology is an exciting frontierwhere astronomy, nuclear physics, and particle physics meet, andwhere we may be able to discover how the universe came to be as itis today. David Schramm Chair Board on Physics and Astronomy

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Cosmology: A Research Briefing Contents  I.   OVERVIEW   1      What Is Cosmology?   1      What's All the Excitement About?   1      The Cosmic Questions   3      Why Do Research in Cosmology?   9      Why Now?   10      Summary   11  II.   THE COSMIC MICROWAVE BACKGROUND RADIATION   12      What Is the Cosmic Microwave Background Radiation?   12      What Do We Learn by Measuring the Properties of the CMBR?   12      The spectrum   12      Why are “bumps” in the CMBR so important?   13      Measurements of Anisotropy   14      Large-scale anisotropy   14      Medium-scale anisotropy   14      Small-scale anisotropy   15  III.   THE LARGE-SCALE STRUCTURE OF THE UNIVERSE   17      Galaxy Maps and Large-Scale Structure   17      What is large-scale structure, and why is it important?   17      Mapping the large-scale structure   17      The importance of uniform galaxy surveys   17      Theory of large-scale structure   18      Cosmic Velocity Flows   19      What are cosmic flows, and why are they important?   19      Measuring cosmic flows   20      Summary and Prospects for Large-Scale Structure   21  IV.   THE DISTANT UNIVERSE   22      Measuring the Cosmological Parameters   22      The Hubble constant, H0   22      The deceleration parameter, q0   23      The density parameter, Ω   24      Deep Imaging of Galaxies   24      Evolution of Large-Scale Structure Back in Time   25      Supernovae, Quasars, and Absorption Line Systems: Probes for Cosmology   25      Gravitational Lenses   27      What are gravitational lenses, and why are they important?   27      Measuring cosmological parameters with gravitational lenses   28

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Cosmology: A Research Briefing  V.   PHYSICS OF THE EARLY UNIVERSE   30      Primordial Nucleosynthesis and Dark Matter   31      Epoch of Inflation and Grand Unified Theories of Matter   32      Particle Theory and Dark Matter Candidates   33      WIMPs   34      Axions   35      Neutrinos   35      Summary of the Study of the Early Universe   36  VI.   CONCLUSION   37     GLOSSARY   38     REFERENCES AND FURTHER READING   41